There have conventionally been proposed eddy current testing probes in which a detection coil is arranged within an exciting coil so that coil planes of the both coils are orthogonal to each other and testing is performed while the detection coil is being rotated (refer to JP-A-2002-214202, for example).
A conventional eddy current testing probe will be described with reference to FIGS. 6A to 6C.
As shown in FIG. 6A, the eddy current testing probe is provided with a pancake-shaped exciting coil EC and a quadrangular (empty square-shaped) detection coil DC, and the both coils are arranged so that coil planes are orthogonal to each other. The detection coil DC is rotated by a motor (not shown) around a central axis P of the exciting coil EC of FIG. 6B in the direction of the arrow. The exciting coil EC is arranged so that a coil plane thereof faces an inspection surface of an object to be inspected T.
To detect flaws F1 to F4 in FIG. 6B in an object to be inspected T, the eddy current testing probe can be placed near the flaws and the detection coil DC can be rotated to detect the flaws F1 to F4 in any orientation. However, the range of the eddy current testing probe in which flaws can be detected is limited to within the range of the rotating detection coil DC. For this reason, when testing is performed along the line L as in FIG. 6C, for example, it is necessary that the eddy current testing probe be intermittently moved to the positions Z1, Z2 and Z3, and that the detection coil DC be rotated each time to perform testing. Therefore, the testing takes a long time.
Hence, there have been proposed eddy current testing probes which move at a prescribed speed while rotating a detection coil in order to permit continuous testing in a wide range (refer to JP-A-2007-248169, for example).
With reference to FIGS. 7A, 7B, and 7C1, 7C2, 7C3 and 7C4, a description will be given of a conventional eddy current testing probe which is moved while rotating a detection coil.
As shown in FIG. 7A, the eddy current testing probe is composed of a probe provided with an exciting coil EC1 and a detection coil DC1 and another probe provided with an exciting coil EC2 and a detection coil DC2; the two probes are mounted side by side on a disk (not shown). The disk moves in the Y-direction while rotating around a central axis P1.
The loci of the detection coils DC1 and DC2 obtained when the eddy current testing probe moves in the Y-direction are as shown in FIGS. 7C1 to 7C4. Specifically, for the distance S over which the eddy current testing probe moves in the Y-direction during one rotation of the detection coils DC1 and DC2, FIG. 7C1 shows loci obtained when S=0.75×W2, FIG. 7C2 shows loci obtained when S=1.0×W2, FIG. 7C3 shows loci obtained when S=1.5×W2, and FIG. 7C4 shows loci obtained when S=2.0×W2. In FIGS. 7C1 to 7C4, the solid lines indicate the loci of the detection coil DC1 and the broken lines indicate the loci of the detection coil DC2. As shown in FIG. 7B, W1 corresponds to the width of the detection coils DC1 and DC2, and W2 corresponds to a width which is twice as large as this width.
In the case of FIGS. 7C1 to 7C3, that is, in the case of the moving distance S=0.75×W2 to 1.5×W2, there is no region where the detection coils do not pass and, therefore, all flaws can be detected without omission in the range of W2, which corresponds to twice the width W1 of each detection coil.
In the case of FIG. 7C4, that is, in the case of the moving distance S=2.0×W2, in the region E2, the loci of the detection coils are sparser and the testing accuracy decreases compared to regions of dense loci. Therefore, it is desirable to use the upper half region not containing the region E2 to perform testing. Note that no loci of the detection coils are indicated in the region E1 because the region corresponds to the start period of the detection coil rotation and hence the detection coils do not pass. When the detection coils have rotated half a rotation after the start of rotation, the loci are as shown in the region E2. In FIG. 7C4, the region E3 is a region where the detection coil DC2 passes and the region E4 is a region where the detection coil DC1 passes. The positions of the region E3 and the region E4 shift from each other by half a rotation (180 degrees) in the Y-direction.